The main goal is to understand how the central nervous system coordinates the large number of degrees of freedom of the arm. The experimental approach includes recording and analysis of the kinematics of multijoint movements. In some cases, a simple mechanical system is used to record the movements. When full arm freedom is required, an optoelectric recording system is used. Work will continue on the following projects on multijoint control. 1. Multijoint movements of the right and left arms are being compared. The comparison includes movements to visual targets, movements which are unexpectedly perturbed, and isometric force production. 2. Studies of the multijoint movements of patients with movement disorders will be continued. To date, there has been concentration on patients with cerebellar disease and Parkinson's disease. Simple movements to visual targets have been emphasized. In the next year, unexpectedly perturbed movements and isometric force production will be studied in these same patient groups, in order to more fully characterize the physiology of these disorders. 3. We are studying the control of multijoint movements in the presence of unexpected mechanical loads. We recently found that with same load types subjects make movements with the same kinematic characteristics as in the unloaded condition. This suggests that there may be a mechanism for rapid real-time trajectory corrections, so that we will investigate this motor-compensation mechanism more fully. 4. The multijoint arm stiffness of patients with a variety of central lesions will be compared to that of normal individuals. By searching for changes in the stiffness due to central diseases, we hope to learn what central structures are involved in stiffness control.